It is the goal of the Center for Radiologic Image Research to increase diagnostic accuracy in Diagnostic Radiology and Nuclear Medicine through the study of radiologic image quality. This involves the generation of new knowledge to explain and evaluate the physical performance of present radiologic imaging methods and devices, the investigation of psychophysical factors linking diagnosis and image quality, and the development of improved imaging methods and devices. The following problems will be studied: 1. Measurement of x-ray spectra. 2. Physical factors affecting radiographic image quality. 3. Study of system and observer performance. 4. Development of new radionuclide imaging agents and procedures. 5. Collimation and detection of radiation in nuclear medicine. 6. Clinical application of research results in diagnostic radiology and nuclear medicine.